Conductive molding compositions and articles molded therefrom

ABSTRACT

Electrically conductive, thermoset molding compositions are disclosed which comprise an unsaturated thermosetting resin, an olefinically unsaturated monomer which is copolymerizable with the thermosetting resin, a thermoplastic additive and carbon black. The carbon black is incorporated in a conductive additive which comprises the thermoplastic additive, the carbon black and, preferably, a lubricant. The electrical resistance of articles molded from the disclosed molding compositions is typically less than about 10 8  ohms/cm 2 .

This application claims the benefit of provisional application No.60/120,677 filed Feb. 19,1999.

FIELD OF THE INVENTION

The present invention relates to conductive, thermoset moldingcompositions and articles made therefrom. More specifically, the presentinvention relates to molding compositions containing thermoplasticadditives comprising conductive carbon black which can impart electricalconductivity to articles molded from the molding compositions.

BACKGROUND OF THE INVENTION

Thermoset molding compositions are commonly used to make a variety ofarticles such as, for example, automotive body panels, truck cabcomponents, appliances, home furnishings, e.g., bathtubs, doors, and thelike. Such molding compositions typically comprise an unsaturatedthermosetting resin, an olefinically unsaturated monomer which iscopolymerizable with the thermosetting resin, a thermoplastic additive,fibrous materials, and various other ingredients, including for example,fillers, mold release agents, and the like.

In some cases, the molding compositions comprise a pigment which impartsa desired color to the molded article. In other cases, the moldedarticles are painted in order to provide the desired color.Electrostatic spray systems are being used more frequently in theindustrial application of primers and paints because of improvements inthe transfer efficiency, that is, the amount of primer or paintdeposited on the article versus the amount of primer or paint sprayed.In systems which do not utilize electrostatics spray processes, “bounceback” and “overspray” can reduce the transfer efficiency. Bounce backoccurs as atomized droplets of paint approach the surface of the articleand an air current rebounding from the same surface deflects thedroplets into a new trajectory away from the article. Overspray occurswhen a portion of the paint is sprayed beyond the article's edge intothe surrounding space.

In electrostatic spray processes, atomized paint droplets are passedthrough an electric field charging the droplets. The droplets are drawnto the article to be painted which is at ground potential. If thearticle cannot conduct electric current, then the article becomesincreasingly charged. This charge buildup on the articles' surfaceeventually repels new incoming charged droplets. This repulsion canlower the transfer efficiency quite dramatically. Therefore, it ishighly desirable in electrostatic paint processes that the surface ofthe article be made conductive.

Both sheet molding compound (“SMC”) and bulk molding compound (“BMC”)are good insulators and have poor electrical conductivity. SMC and BMCmolded articles can be made conductive by incorporating a conductivematerial, e.g., carbon black, into the molding composition or byapplying a conductive coat (known in the art as a “dust coat”) on themolded article. The incorporation of carbon black in its neat form intomolding compositions is generally undesired in the art because handlingcarbon black presents significant housekeeping problems and healthconcerns. Applying a dust coat is also generally undesirable because itadds an additional step to the painting process which often increasescosts.

Accordingly, improved molding compositions are desired to provideelectrically conductive molded articles which are suitable forelectrostatic painting. Desirably, the improved molding compositionswould allow molders of articles to avoid the necessity of handling neatcarbon black and avoid the use of a dust coat in the electrostaticpainting process.

SUMMARY OF THE INVENTION

By the present invention, improved molding compositions suitable formanufacturing electrically conductive articles are provided. As aresult, articles molded from the molding compositions of the presentinvention can be painted by electrostatic painting processes which canlead to enhancements in the transfer efficiency of the paint to thearticle, i.e, a reduction in bounce back and overspray and acorresponding reduction in the amount of volatile organic compoundsreleased to the environment.

In accordance with the present invention, electrically conductive,carbon black is incorporated into compositions comprising athermoplastic polymer (hereinafter referred to as “conductiveadditive”). The conductive additives are preferably prepared in the formof pellets or extrudate prior to their addition to the moldingcompositions. Quite advantageously, the incorporation of the conductivecarbon black into the conductive additive avoids the necessity ofhandling carbon black in its neat form. Also, the amount of carbon blackintroduced into the molding compositions can be more accuratelycontrolled.

Quite surprisingly, it has been found in accordance with a preferredaspect of the present invention that by adding a lubricant, e.g., zincstearate, during the manufacture of the conductive additives, theelectrical conductivity of the conductive additive and the resultingmolding composition in which it is incorporated, and articles moldedtherefrom, can be enhanced.

DETAILED DESCRIPTION OF THE INVENTION

The carbon black suitable for use in accordance with the presentinvention can be any carbon black material which conducts electricity.Typically, the conductive carbon black will be in aggregate form, suchaggregates having a particle size of from about 10 nanometers (“nm”) to75 nm, preferably about 15 to 40 nm, and more preferably about 20 to 30nm. A typical aggregate of carbon black comprises a cluster, or bunch ofparticles ranging from about 1 micron (“μm”) to 10 μm. Desirably theaggregates are touching or in close proximity to another aggregate inorder for electrons to flow, known in the art as “tunnelling”. Withoutbeing bound to any particular theory, this is believed to be fundamentalto the mechanism of electrical conductivity. The surface area of thecarbon black particles typically ranges from about 80 meters squared pergram (“m²/g”).to 1400 m²/g preferably from about 130 to 1300 m²/g andmore preferably from about 600 to 1,000 m²/g.

The carbon black has a high pore volume if the aggregates compriseparticles arranged in a highly branched structure. This is referred toin the art as a “high structure” and is very desirable for enhancingelectrical conductivity. The degree of structure, low or high, istypically determined by the Di-butyl phthalate (“DBP”) absorption valuewhich has units of milliliters of DBP per 100 g carbon black (“ml/100 gcarbon black”). Higher absorption of DBP means a higher structure. DBPabsorption typically ranges from about 65 ml/100 g to 500 m/100 g,preferably from about 120 ml/100 g to 400 ml/100 g and more preferablyfrom about 140 ml/100 g to 385 ml/100 g.

Furthermore, the surface chemistry, or % volatility, is important ifmaximum conductivity is to be achieved. The “% volatility” refers to theoxygen containing functional groups present at the surface of the carbonblack. A high concentration of these organic, functional groups may actas a barrier to the electron tunneling effect. If the electron tunnelingis essential for efficient conductivity, the % volatility should beminimized. The % volatility of carbon black can typically range as highas 22% to as low as 0.4%. Generally, carbon black with a % volatility ofless than about 1.0% is desired. Carbon black suitable for use inaccordance with the present invention is available, for example, fromAkzo Nobel Chemicals of Dobbs Ferry, N.Y., Cabot Corp. of Billerica,Mass. and Degussa Corp. of Rochelle Park, N.J. Further detailsconcerning the selection of carbon black are known to those skilled inthe art.

The thermoplastic additives suitable for use in accordance with thepresent invention can be any materials which have the desireddimensional control effect, e.g., shrinkage control, on the moldedarticle. Typical of such thermoplastic additives include for example,polystyrene, polyvinyl acetate homopolymers and copolymers, e.g., vinylacetate copolymerized with acrylic acid, crotonic acid, vinyl chloride,polyurethanes, saturated straight-chain and cyclic polyesters, polyalkylacrylates, or methacrylates and the like. Polyvinyl acetates andmixtures thereof with other thermoplastics are preferred thermoplasticadditives for use in accordance with the present invention.

The weight average molecular weights of the thermoplastic additives ofthe present invention are from about 10,000 to 250,000, preferably fromabout 25,000 to 200,000 and more preferably from about 50,000 to 180,000grams per gram mole (“g/g mole”). As used herein, the term “averagemolecular weight” means weight average molecular weight. Methods fordetermining weight average molecular weight are known to those skilledin the art. One preferred method for determining weight averagemolecular weight is gel permeation chromatography. The thermoplasticadditives can be used in conjunction with lower molecular weightmaterials which can enhance their shrinkage control ability such asepoxys, lower reactivity secondary monomers and others. Examples of suchapproaches are disclosed in U.S. Pat. Nos. 4,525,498, 4,755,557, and4,374,215.

One or more thermoplastic additives may be employed in the compositionsof the present invention. Further details of the preferred thermoplasticadditives suitable for use in accordance with the present invention aredescribed, for example, in U.S. Pat. No. 4,172,059. Such thermoplasticadditives are commercially available or alternatively can be prepared bythose skilled in the art.

The lubricants suitable for use in the present invention can be anymaterials which are effective to enhance the electrical conductivity ofthe molded articles. Without being bound to any particular theory, it isbelieved that mechanical degradation of the carbon black aggregates canoccur during the manufacture of the conductive additives, e.g., underthe mixing shear and pressure that occurs, for example, during the meltextrusion of the thermoplastic additive with the carbon black. It isbelieved that such mechanical degradation can reduce the electricalconductivity of the conductive additives and hence, reduce theelectrical conductivity of the articles molded from molding compositionscomprising the conductive additives. Quite surprisingly in accordancewith the present invention, it has been found that the incorporation oflubricants during the combination of the carbon black particles with thethermoplastic additive can enhance the electrical conductivity of theresulting conductive additives.

Preferably, the lubricants are selected from the group consisting offatty acids and their metallic counterparts, for example, metallicstearates, polyalkylene glycols, polyalkylene oxides, detergents,phosphoric acid esters, polyether polyols, ethoxylated fatty acids, andmixtures thereof. Zinc stearate is an especially preferred lubricant foruse in accordance with the present invention.

In making the conductive additives, the thermoplastic polymer or mixtureof thermoplastic polymers is preferably combined, in a melted state,with the conductive carbon black and an effective amount of thelubricant in order to enhance the electrical conductivity of theconductive additive.

The conductive additive typically comprises from about 5 to 40, moretypically from about 5 to 39, most typically from about 5 to 30,preferably from about 10 to 25 and more preferably from about 15 to 20weight percent carbon black, typically from about 60 to 95, moretypically from about 60 to 94, preferably from about 67 to 88 and morepreferably from about 75 to 85 weight percent of the thermoplasticadditive, and typically from about 0 to 35, more typically from about 1to 10 preferably from about 2 to 8 and more preferably from 4 to 6weight percent of the lubricant, said percentages based on the totalweight of the conductive additive.

The conductive additive can be made by any technique which is effectiveto combine the carbon black, thermoplastic additive and lubricant.Typical techniques include for example, mixing, rolling and melt mixingvia extrusion, with extrusion being preferred. Suitable extrudersinclude for example, twin screw extruders available from Berstorff Corp.of Charlotte, N.C., Werner & Pfleiderer of Ramsey, N.J., or kneaders,available from Buss America of Bloomingdale, Ill. Further detailsconcerning suitable extruders are known to those skilled in the art. Thetemperature at which the combination of ingredients is conducteddepends, for example, on the particular thermoplastic additive used.Typically, the temperature will range from about 100 to 200° C. andpreferably from about 130 to 160° C. The pressure under which the meltmixing is conducted is not critical. Typical pressures range from about100 to 2,000, preferably from about 300 to 1,000 psia.

Preferably, the shearing which occurs during melt mixing, e.g.,extrusion, is reduced by the presence of the lubricant in accordancewith the present invention. Preferably, the conductive carbon blackaggregates will be substantially free of mechanical degradation afterextrusion. A convenient method for melt mixing in the laboratory is theuse of a Brabender torque rheometer available from Brabender Company,South Hackensack, N.J. It is also a convenient way to measure PeakTorque. As used herein, the term “Peak Torque” means the highest torquereading indicated after the carbon black has been added to the polymer,measured at 160° C. and 60 revolutions per minute (“rpm”) using aBrabender torque rheometer. It has been found in accordance with thepresent invention that the peak torque should be minimized during meltmixing and preferably should be less than about 1,000 Meter-gram (“M-g”)and more preferably less than about 750 M-g.

The conductive additive may be prepared in any convenient form, e.g., aspellets, extrudate or spheres. Typically, the conductive additive isprepared as pellets having a size ranging from about 1.5 millimeters(“mm”) to 4mm, and preferably from about 2 mm to 3 mm in diameter.

Further details on extrusion and other melt mixing techniques andeffective conditions for making the conductive additives for use inaccordance with the present invention are known to those skilled in theart.

The unsaturated thermosetting resins suitable for use in accordance withthe present invention include those unsaturated polymeric materialswhich can be crosslinked to form thermoset articles. Typically, theunsaturated thermosetting resins have a weight average molecular weightof at least 500, preferably from about 500 to 10,000 g/g-mole.

Typical unsaturated thermosetting resins include, for example, epoxydiacrylates, polyester diacrylates, polyurethane diacrylates, acrylatecapped polyurethane polyacrylates, acrylated polyacrylates, acrylatedpolyethers and the like. Especially preferred thermosetting resinsinclude polyesters and vinyl esters. As used herein, the term“polyesters” also includes vinyl esters. Typically, the unsaturatedthermosetting resins are; (i) a polyester resin comprising variouscombinations of anhydrides, such as maleic anhydride, and dicarboxylicacids, such as adipic acid or isophthalic acid, condensed with variousdiols such as propylene glycol, ethylene glycol, or 1,4-butanediol; or(ii) a vinyl ester resins comprising Novolac resins such as Derakane 780or Bisphenol A based such as available from The Dow Chemical Company,Midland, Mich. Derakane 411-350. Such unsaturated thermosetting resinsare commercially available or alternatively can be readily prepared bythose skilled in the art. Examples of suitable unsaturated thermosettingresins for use in accordance with the present invention are describedfor example in U.S. Pat. Nos. 4,172,059 and 4,942,001.

One or more unsaturated thermosetting resins may be employed in themolding compositions of the present invention. The total amount ofunsaturated thermosetting resins in the molding compositions of thepresent invention is typically from about 15 to 80 weight percent,preferably from about 20 to 60 weight percent, and more preferably fromabout 25 to 50 weight percent based on the weight of the unsaturatedthermosetting resin, conductive additive and olefinically unsaturatedmonomer. Further details concerning the selection and amounts ofunsaturated thermosetting resins are known to those skilled in the art.

The olefinically unsaturated monomers (also referred to herein as“crosslinking monomers”) suitable for use in accordance with the presentinvention include materials which are copolymerizable with theunsaturated thermosetting resins. The monomer also serves the itsinteraction with the other components of the molding composition.Preferably, the olefinic unsaturation is due to ethylenic unsaturation.Typical olefinically unsaturated monomers include, for example, styrene,vinyl toluene isomers, methyl methacrylate, acryl nitrile andsubstituted styrene such as, for example, chlorostyrene andalphamethylstyrene. Multifunctional monomers, such as, for example,divinylbenzene or multifunctional acrylates or methacrylates may also beemployed. Styrene is a preferred monomer for use in the compositions ofthe present invention.

One or more olefinically unsaturated monomers may be used in the moldingcompositions of the present invention. Typically, the total amount ofthe olefinically unsaturated monomers is from about 1 to 80 weightpercent, preferably from about 5 to 50 weight percent, and morepreferably from about 15 to 25 weight percent based on the weight of theunsaturated thermosetting resin, conductive additive and crosslinkingmonomer. Such monomers are readily commercially available. Usually, thethermosetting resins are dissolved in the olefinically unsaturatedmonomer to contain about 50 to 75 weight percent of the thermosettingresin. This is often done for ease of handling. Further detailsconcerning the selection and amounts of the olefinically unsaturatedmonomers are known to those skilled in the art.

Typically, the total amount of the conductive additive in the moldingcompositions is from about 3 to 30 weight percent, preferably from about5 to 25 weight percent and more preferably from about 8 to 20 weightpercent based on the weight of the unsaturated thermosetting resin,conductive additive and crosslinking monomer.

Preferably, the total amount of carbon black in the molding compositionis from about 0.1 to 10 weight percent, preferably from about 0.5 to 5weight percent, and more preferably from about 0.5 to 1.5 weight percentbased on the weight of the unsaturated thermosetting resin,thermoplastic additive and crosslinking monomer.

Reinforcements are also often employed in the molding compositions ofthe invention and can be, for example, any of those known to the art foruse in molding compositions. Examples of such materials are glass fibersor fabrics, carbon fibers and fabrics, asbestos fibers or fabrics,various organic fibers and fabrics such as those made of polypropylene,acrylonitrile/vinyl chloride copolymer, and others known to the art.These reinforcing materials are typically employed percent, based on thetotal weight of the molding composition and preferably 15 to 50 weightpercent.

The molding compositions of the invention may also contain one or moreother conventional additives, which are employed for their knownpurposes in the amounts known to those skilled in the art, e.g., about0.5 to 10 weight percent based on the total weight of the moldingcomposition. The following are illustrative of such additives:

1. Polymerization initiators such as t-butyl hydroperoxide, t-butylperbenzoate, benzoyl peroxide, t-butyl peroctoate, cumene hydroperoxide,methyl ethyl ketone peroxide, peroxy ketals, and others known to theart, to catalyze the reaction between the olefinically unsaturatedmonomer and the thermosetting resin. The polymerization initiator isemployed in a catalytically effective amount, such as from about 0.3 toabout 3 weight percent, based on the weight of the unsaturatedthermosetting resin, conductive additive and crosslinking monomer.

2. Fillers such as clear, alumina trihydrate, silica, calcium carbonate,and others known to the art;

3. Mold release agents or lubricants, such as zinc stearate, calciumstearate, and others known to the art;

4. Viscosity reducing additives;

5. Thickeners, such as magnesium oxide, magnesium hydroxide, calciumoxide, calcium hydroxide, zinc oxide, barium oxide and mixtures thereof;and

6. Water.

The molding compositions of the present invention can be prepared bymethods known to those skilled in the art, such as for example, mixingthe components in a suitable apparatus such as Hobart mixer attemperatures on the order of about 20 to 50° C. The components may becombined in any convenient order. Generally, it is preferable that thethermosetting resin and conductive additive are added in liquid form bypreparing a solution thereof in the crosslinking monomer. All the liquidcomponents are then typically mixed together before adding the fillers,thickening agents and optional ingredients.

Once formulated, the molding compositions can be molded into thermosetarticles of the desired shape, e.g., automotive fenders, hoods,appliances, bathtubs, doors, and the like. The specific conditions usedin the molding process depend on the composition being molded as well asupon the nature of the particular articles desired, the details of whichare known to those skilled in the art. Typical molding pressures for usein accordance with the present invention are from about 30 to 2,000psia, preferably from about 100to 1500 psia, and more preferably fromabout 200 to 1000 psia. Suitable molding temperatures are from about 80to 180° C., preferably from about 100 to 160° C. and more preferablyfrom about 120 to 150° C. Typical molding time periods range from about0.5 to about 5 minutes or longer.

The molding compositions of the present invention are suitable for use,for example, as sheet molding compounds and bulk molding compounds. Forexample, sheet molding compound can be produced by laying down a firstlayer of the molding composition, i.e., paste, on a first layer ofpolyethylene film or the equivalent thereof, laying on this first layerof the paste filler reinforcements such as chopped glass fibers, andlaying thereover a second layer of the paste. The two layers of thepaste with the filler reinforcements sandwiched therebetween are thentopped with a second sheet of polyethylene film and the resultingcomposite (sheet molding compound) is stored. Bulk molding compound canbe produced by the use of sigma blade mixers, plow blade mixers,kneaders and the like. Further details concerning the manufacture,handling and use of sheet molding compounds and bulk molding compoundsare known to those skilled in the art.

The articles molded from the molding compositions of the presentinvention typically have an surface resistivity of less than about 10⁸,preferably less than about 10⁷ and more preferably less than about 10⁶to 10⁴ ohms per square centimeter (ohms/cm²). Molded sheets of theconductive additive preferably, have a surface resistivity of less thanabout 10 ohms/cm² and more preferably less than about 5 ohms/cm².Techniques for measuring surface resistivity are known to those skilledin the art, see, for example ASTM procedure D257. As a result, thearticles molded from the molding compositions of the present inventionare particularly suitable to be coated, e.g., painted, by electrostaticpainting processes. In comparison, the surface L resistivity of moldedarticles which do not comprise carbon black is typically greater thanabout 10¹² ohms/cm². Details concerning electrostatic painting processesare known to those skilled in the art.

The following examples are provided for illustrative purposes and arenot intended to limit the scope of the claims which follow.

Definitions

The following materials were used in the examples set forth below:

p-BQ—A five percent solution of parabenzoquinone in diallylphthalate.

Calcium Carbonate—A calcium carbonate filler having a particle size of 5microns supplied by Georgia Marble of Kennesaw, Ga. and sold under thedesignation CalWhite II™.

PG 91148—A mixture of magnesium and calcium hydroxides dispersed in alow molecular weight polyester available from Plasticolors, Inc. ofAshtabula, Ohio

Orthophthalic UPE—an unsaturated thermosetting resin (polyester) resinthat is modified using typically 15-30 mole % orthophthalic acidsubstituted for maleic anhydride available from Ashland Chemical,Dublin, Ohio, as Q6710 (or MR 13031) and contains styrene monomer.

LPS—4015—A carboxylated poly(vinyl acetate), having a weight averagemolecular weight of about 75,000 to 100,000 g/mole available from UnionCarbide Corp., Danbury, Conn.

zinc stearate—an internal mold release available from Syntheticproducts, Cleveland, Ohio.

VR-3—a fatty acid viscosity reducer available from Union CarbideCorporation, Danbury, Conn.

Conductive Carbon Black—A fine-particle form of microcrystalline carbon,available from Degussa Corp. of Rochelle Park, N.J.

tBIC—a peroxide initiator, t-Butyl-Isopropyl-Monoperoxy Carbonate,available from Atochem North America, Inc., Buffalo, N.Y.

DVB-CP—Chemically pure grade divinyl benzene available from Dow Chemicalof Midland, Mich.

Styrene—an olefinically unsaturated aromatic monomer available fromAshland Chemical of Dublin, Ohio.

Modifier E—an inhibitor solution consisting 5% solution ofp-benzoquinone in Diallyl phthalate available from Ashland Chemical ofDublin, Ohio.

Ionol—Butylated hydroxy toluene inhibitor available from EastmanChemical Company of Kingsport, Tenn.

Byk 995—a proprietary viscosity reducer available from Byk Chemie ofCanton, Ohio.

XVR-10—a thickening control agent comprising a liquid fatty acidavailable from Union Carbide Corp., Danbury, Conn.

General Procedure for Preparation of Bulk Molding Compound (BMC)Formulations

All the liquid components were weighed individually into a Hobart mixingpan placed on a Toledo balance. The pan was attached to a Model C-100Hobart mixer (in a hood). The agitator was started at slow speed, thenincreased to medium speed to completely mix the liquids over a period of3-4 minutes. The agitator was then stopped and the internal mold releaseagent and/or fatty acid was next added to the liquid from an ice creamcarton. The Hobart mixer was restarted and the mold release agent mixedwith the liquid until it was completely wet out. The filler was nextadded to the pan contents (agitator off) then mixed, using medium tohigh speed, until a consistent paste was obtained. The mixer was againstopped and the weighed amount of thickening agent was mixed into thepaste over a period of 2-3 minutes, the mixer was again stopped and ˜175grams of the paste were removed from the pan (using a large spatula) andtransferred to a wide-mouthed 4 oz. Bottle. This paste sample was storedin the capped bottle at room temperature and the viscosity was measuredperiodically using a Model HBT 5× Brookfield Synchro-Lectric Viscometeron a Helipath Stand. Typical viscosities ranged from 10×10⁶ to 80×10⁶centipoise (“cP”).

After removal of the paste sample, the contents were reweighed andstyrene loss made up, the chopped glass fibers were added slowly (froman ice cream carton) to the pan with the mixer running on slow speed.The mixer was run for ˜30 seconds after all the glass was in the paste.This short time gave glass wet out without glass degradation. The panwas then removed from the mixer and separate portions of the BMC mix of˜450 grams each were removed using spatulas and transferred to aluminumfoul lying on a balance pan (balance in the hood). The mix was tightlywrapped in the aluminum foil (to prevent loss of styrene viaevaporation) and stored at room temperature until the viscosity of theretained paste sample reached molding viscosity. The weight of the BMCadded to the foil varies with the molding application.

General Procedures for Preparation of Sheet Molding Compound (SMC)Formulations

All the liquid components were weighed individually into a 5 gallon opentop container placed on a Toledo balance. The contents of the containerwere the mixed (in a hood) with a high speed Cowles type dissolver. Theagitator was started at a slow speed, then increased to medium speed tocompletely mix the liquids over a period of 2-3 minutes. The moldrelease agent and/or fatty acid was next added to the liquids from anice cream carton and mixed until completely dispersed. The filler wasnext added gradually from a tared container until a consistent paste wasobtained and the contents were then further mixed to a minimumtemperature of 32° C. The thickener was next mixed into the paste over aperiod of 2-3 minutes, the mixer was stopped and ˜175 grams of the pastewas removed from the container and transferred to a wide-mouthed 4 oz.Bottle. The paste sample was stored in the capped bottle at roomtemperature and the viscosity measured periodically using a Model HBT 5×Brookfield Synchro-Lectric Viscometer on a Helipath Stand.

The balance of the paste was next added to the doctor boxed on the SMCmachine where it was further combined with fiber glass (˜1″ fibers). Thesheet molding compound (SMC) was then allowed to mature to moldingviscosity and then molded into the desired article.

Molding Facilities

18″×18″×0.120″ Test Panels

Flat panels were molded on a 75 TON Queens Hydraulic press. The presscontained a matched dye set of 18″×18″ chrome plated molds. The femalecavity was installed in the bottom and the male portion was at the top.Both molds were electrically heated and were controlled on separatecircuits so that the molds could be operated at different temperatures.The top and bottom temperature was 148° C. The molding pressure whichcan be varied from 0-75 TON was run at 1000 psig. The cure time was 90seconds and the closure speed was 12 inches/minute. The charge weightwas 1200 grams. The molds did not contain ejector pins; therefore, themolded panel was removed with a rubber suction cup and the use of astream of air. The panels were laid on a flat surface, weighted to keepthem flat and allowed to cool overnight

The electrical surface resistivity was measured with an Electro-techSystems wide range resistance meter, model 872A that was equipped with aconcentric electrical resistivity probe, model 803B. The measurementswere performed in accordance with ASTM D 257. A surface resistivitymeasurement at 10 volts was made by placing the resistivity probe on theflat surface of a test panel. The decade switch of the resistance meterwas adjusted to within the range of the analog meter. The surfaceresistivity, Ω/sq., (ohms per square centimeter), then was readdirectly. The reported surface resistivity values of Example 3 are anaverage of nine readings on each test panel.

EXAMPLE 1 Preparation of Conductive Additive

The Brabender Torque Rheometer is a machine able to simulate the hotmelt mix conditions of a twin screw extruder and is capable of producingpolymeric mixtures on a laboratory scale. Temperature, mix time, and rpmof the mixer can be varied as desired. The dependent variable, mixertorque, is indicated digitally and can be tracked via a strip chartrecorder.

The LPS-4015 and zinc stearate were first weighed in the properproportions to provide the compositions set forth in Table 1 andintroduced into the Brabender mix chamber via a load funnel. Thematerials were mixed until the torque curve “lined out to insure ahomogeneous dispersion. This torque value was recorded as the initialtorque. The conductive carbon was added and the polymer peak temperatureand the Peak Torque, the highest torque obtained, were recorded. Thespeed was adjusted after 5 minutes to 100 rpm. At a total mix time of 10minutes, the mixing chamber was disassembled, the mixture was removedand allowed to cool. Table 1 displays the various compositions of theconductive additives.

TABLE 1 Brabender Hot Melt Mixing of Conductive Additives Mix ConditionsTemperature - 160° C. Initial RPM - 60 for 5 min. Final RPM - 100 for 5min. Total Mix Time - 10 min. Conductive Additives, wt. % Sample No. 1 23 4 5 LPS-4015 84 83 82 80 78 Conductive Carbon Black 16 16 16 16 16Zinc Stearate 0 1 2 4 6

EXAMPLE 2 Preparation of Molding Compositions

Table 2 below shows the formulas used for examining the variouscompositions of conductive additives produced in Example 1.

TABLE 2 Formulations of Conductive Molding Compounds (weight part per100 weight parts of Resin) Sample No. 6 7 8 9 10 11 Ortho Polyester 6060 60 60 60 60 Resin Neulon Preblend T 4 4 4 4 4 4 DVB CP 3.9 3.9 3.93.9 3.9 3.9 styrene 29 29 29 29 29 29 Modifier E 0.5 0.5 0.5 0.5 0.5 0.5Byk 995 3.3 3.3 3.3 3.3 3.3 3.3 Ionol (10% in 1 1 1 1 1 1 styrene)XVR-10 2 2 2 2 2 2 Conductive Additive 16 — — — — — #1 ConductiveAdditive — 16 — — — — #2 Conductive Additive — — 16 — — — #3 ConductiveAdditive — — — 16 — — #4 Conductive Additive — — — — 16 — #5 LPS-4015 —— — — — 13.4 Conductive Carbon — — — — — 2.6 Black All above componentsmixed until conductive additive was dissolved tBIC, phr 2.2 2.2 2.2 2.22.2 2.2 Zinc Stearate, phr 2 2 2 2 2 2 Calcium Carbonate, 180 180 180180 180 180 phr PG 91148 16 16 16 16 16 16 1/2″ chopped Fiberglass @ 15%by wt.

All parameters were kept constant except the conductive additive. Notethat Sample 11 is the control where the conductive carbon was addeddirectly to the resin formula and dispersed at that point. Thisconductive carbon was the same as in the conductive additives, but wasnot subjected to the high mix shear of the polymer melt and itsdegrading effects. Also, all components were pre-mixed until solids weredissolve/dispersed using a high shear Cowles blade. The polymerizationinitiator, tBIC, was added/mixed and then followed by the addition ofzinc stearate. The paste was transferred to the Hobart mixer wherecalcium carbonate was added and mixed at high speed. The thickener,PG-91148, was added/mixed under medium speed. Finally 15 wt. % offiberglass was added, mixed and wetted out under low speed. The moldingcompound was then weighed out to the specified value, wrapped andallowed to maturate for two days before molding.

EXAMPLE 3 Electrical Resistance Measurements

Panels made in accordance with the compounding procedure described abovewere molded and tested for electrical conductivity. The results of thecharacterization are set forth in Table 3.

Example 3 gives Peak Torque recorded during the mixing of the conductivecarbon into the polymer melt. Sample 6, which contains the conductiveadditive where no zinc stearate was used as a processing aid, had thehighest Peak Torque and as expected the highest surface resistivity. Asone progresses from Sample 7 through Sample 10, the level of theprocessing aid, zinc stearate, increases, the Peak Torque decreases, andthe surface resistivity decreases as well. Sample 11 has no peak torquevalue because the conductive carbon black and the thermoplastic lowprofile additive were introduced directly into the molding formula. Thisis a best case condition that gave the least surface resistivity becausethe conductive carbon was not subjected to the mechanical degradation ofthe polymer melt mixing process. Indeed, the surface resistivity wasfound to be 1×10⁴ ohms.cm², the lowest recorded.

TABLE 3 Surface Resistivity versus Peak Torque Sample No. 6 7 8 9 10 11Peak Torque, 1250 950 748 698 680 — meter²/gram Surface 4.0 × 1.3 × 1.3× 7.8 × 6.3 × 1 × Resistivity, 10⁵ 10⁵ 10⁵ 10⁴ 10⁴ 10⁴ ohms/cm²

EXAMPLE 4 Electrostatic Painting of SMC Panels

SMC of a similar composition as the BMC panels described above werepainted electrostatically in order to evaluate a conductive panel versusa non-conductive panel in the electrostatic and non-electrostaticpainting processes.

In both processes an air assisted painting was used in the determinationof transfer efficiency (“TE”). TE is defined as the percentage of solidcoating material transferred to a substrate. TE can be determined if thevalues four major variables are known: line speed, target width, flowrate and total solids.

Line speed was determined by the movement of the application device(Nordson SCF AE-1) past the substrate. The spraymation moves theapplication device from left to right while valving open across thetarget. The movement of the device is a measure within the spraymationand electronically displayed in inches/minute.

Standardization is done manually by timing the movement of the spraydevice over a known distance, i.e. 24 inches, and manually calculatedbefore each run.

Target Panel Width is merely the width of the SMC panel, 18 inches.

Flow Rate is the difference between two mass flow meters in a timedperiod to determine flow rate of the nozzles while the applicationdevice passed in front of the part. The UNICARB® system, available fromUnion Carbide Corporation, Danbury, Conn., which is based on the use ofsuper critical carbon dioxide (CO2) as a solvent, was used in thisexperiment. To determine the CO₂ concentration a sample (Hoke) cylinderwas used. The amount of total flow difference of the mass flow meterswas then multiplied by the CO₂ concentration. This gave the volume ofcoating sprayed out of the application device during a timed interval.Mass flow is the calculated in /min. sprayed.

Total solids were determined by backing a 0.25 g-0.50 g sample of thecoating in aluminum sample pans for 60 minutes at 110° C.

The TE was calculated as below:

Line Speed seconds (“s”)/foot (“ft”)×Panel Width (ft)×Flow Rate(g/s)×Total Solids=Solids Sprayed (g)

The tare weight (g) of the target panel is determined. The panel is thencoated, baked and then weighed (Solids+Tare weight (g)). The amount ofsolids applied to the panel is then determined.

Solids Applied (g)=(Solids+Tare weight (g))−(Tare Weight (g))

TE (%)=(Solids Applied (g)/Solids Sprayed (g))×100

The first column of Table 4 shows the results of painting the panelselectrostatically (ES). The TE of the conductive SMC panel is 44.4%versus that of the non-conductive SMC panel, 10.1%. The low TE of thenon-conductive SMC panel appears to be the result of the charged paintdroplets being repelled by the increasingly charged panel's surface,i.e., because the SMC is non-conductive a static charge cannot drain toground fast enough to prevent charge accumulation. The next column isthe non-ES painted panels and, as expected, the TE values are virtuallythe same for both types of SMC. However for the non-conductive, non-ESpanel the TE is 33.3% or about 10% less than the conductive, ES paintedpanel.

TABLE 4 Transfer Efficiency Study of Painted SMC Panels Non- Electro-static Electrostatic (control) Conductive 44.4% 33.3% Non-Conductive10.1% 34.4%

In addition to the specific aspects of the invention described above,those skilled in the art will recognize that other aspects are intendedto be included within the scope of the claims which follow.

I claim:
 1. A process for making an electrically conductive compositioncomprising combining in an extruder a melted thermoplastic additivehaving a weight average molecular weight of from about 10,000 to 250,000grams per gram mole with carbon black and from 1 to 10 weight percent ofa lubricant based on the total weight of the thermoplastic additive,carbon black and lubricant, and extruding a mixture of components. 2.The process of claim 1 wherein the combining is conducted at atemperature of from about 100 to 200° C.
 3. The process of claim 1wherein the combining is conducted at a pressure of from about 100 to2,000 psia.
 4. The process of claim 1 wherein the combining is doneunder shearing conditions.
 5. The process of claim 4 wherein the PeakTorque of the composition is less than about 100 M-g.
 6. The process ofclaim 1 wherein the lubricant is selected from the group consisting offatty acids and their metallic counterparts, polyalkylene glycols,polyalkylene oxides, detergents, phosphoric acid esters, polyetherpolyols, ethoxylated fatty acids and mixtures thereof.
 7. The process ofclaim 6 wherein the lubricant is zinc stearate.
 8. The process of claim1 wherein the thermoplastic additive is present in an amount of about 60to 94 percent by weight and the carbon black is present in an amount ofabout 5 to about 40 percent by weight, wherein the percentages are basedon the total weight of the thermoplastic additive, carbon black andlubricant.
 9. A process for preparing a molding composition whichcomprises contacting one or more electrically conductive compositionsaccording to claim 1, one or more unsaturated thermosetting resins andone or more olefinically unsaturated monomers which are copolymerizablewith the unsaturated thermosetting resins.
 10. The process according toclaim 9 wherein the electrically conductive composition and theunsaturated resin are contacted in liquid form.
 11. The process of claim10 wherein the electrically conductive composition and the unsaturatedthermosetting resin ore dissolved in olefinically unsaturated monomersprior to contacting.
 12. The process of claim 11 wherein the contactedsolutions of electrically conductive compositions and the unsaturatedthermosetting resins are mixed after contacting.
 13. The process ofclaim 12 wherein fillers and thickening agents arc added after mixingthe electrically conductive composition and unsaturated thermosettingresins.